Microphone



Jan. 20, 1953 c. K. STEDMANl ETAL 2,626,380

MICROPHONE Filed Sept. 1l, 1943 INVENToRs GEC/L -K. STE'DAMN BY FREDERICK H. SMIT/l ATTORNEY Patented Jan. 20, 1953 UNITED. STA-TES OFFICE...

MICROPHONE Cecil K.` Stedman, Watertown, and Frederick H; Smith, East Natick, Mass., assignors` to thef United States of America as representedv by the Secretary of the Navy Appiicationscptemhcr 11, 1943,;SeriaLNo..5ll2,076

1 Claim.

This, invention relatesto microphonestand more` particularly tov a novel' magnetostrictive-microf-` phone of simpleandcompact constructioniwhich is sensitive anddirectionally selective in .opera-- mountedat its base end on a vibratoryelement or diaphragm" and supporting at Vits .reduced end a ycoaxial magnetostriction tube.

Another objecty of the invention is to provide` a microphone ofthe character described in which. the. magnetostricticn tube is disposedwithin an independently supported coilV and contains a polarizing magnet; whereby compressional waves transmitted tothetube from the base of' the conical member, cause. the generation of an electromotive force in the coil corresponding in magnitude to the intensity of the compressional waves.

A further object of the invention resides in the provision of a novel magnetostrictive microphone for use in automatically directedv antisubmarine torpedoes .to detect compressional waves of small intensity from the submarine, which is of. rugged construction and occupies alrelatively small space inthe torpedo.

These and` other objects ofthe invention may be better understood by reference to the-.accompanying drawing, in which:

Fig. l is .a side view, partly insection, ofpart .of a torpedo employinghone form of the new microphone;

Fig. 2.is an enlarged longitudinal sectionalyiew of theheadaportion of .the.torpedogshowingeone of the microphones illustrated in Fig. 1

Fig. 3 is a detail View in section showing the connection between the magnetostriction tube and the conical member illustrated in Fig. 2;

Fig. 4 is an exploded perspective view of part of the microphone shown in Fig. 2, and

Fig. 5 is a sectional view on the line 5-5 in Fig. 2.

The new microphone, as illustrated, is in a form suitable for detecting high-frequency compressional waves transmitted through water. While the microphone is adapted for various uses, it may be used to particular advantage in an electrically controlled azimuth steering system for torpedoes, as disclosed in a copending application of C. K. Stedman et al., Serial No. 502,075, led September 11, 1943.

Referring'tothe drawing, the torpedocomprisesv a cylindrical hull It) and a generally hemispherical head I I, which may be. spun from sheet metal. The headv isconnectedto` the frontend of` the:

hull in any suitable manner. as by means of'bolts. lidisposed in an annular recess in the head.v A

fuse i3. is mounted on theinnerwall of the head and disposed axially therein, and on opposite sides of the fuze: are' two microphones; or'y ears I4' and tia. made inaccordance with thev invention'. The microphones are disposed' in a. common horizontal plane with their. axes converging toward the fuze axis at an angle of substantially 45' degrees, whereby each microphone is operable in anoptimumdirection to the exclusion ofthe other.. The highY explosive charge (not shown). may be packed around the fuze I 3 andthe microphones. Sincethe.microphones. it andjMa. are identical. in construction, a descriptionof one. of them. will suiiice.

The microphone. comprises a solid member I 6 of generallyv ,conical .shape which is. made of metal, such as:l brass. AtA its base, the conical member Itis carefully. tted to the innerface of the hemisphericalheadY Mythe vcone being secured` to the head. inanysuitable manner, as by. meansoi a screw il. threaded into the central portion of the cone... Inttingthe base of thecone to the inner face-of the-head II, one of theY opposing. surfaces may be coated with. lampblack.. or the like, and the. surfaces pressed together to make. an. imprint of the uncoated.surface..v The surface not having the lampblackmay thenbescraped in accordance Withmheimprint, toproyidea closer fit... This tting operation isdesirable. for.. the reason that thehead Il. is.not.likely to have a perfectly true spherical. form.. After the fitting Aoperation .is completed, the base .ci the cone lli andthe opposing surface of the head II are preferably heated, coated thinly with soft solder and pressed tightly together, the screw Ii being in place but not completely tightened. The cone I6 is then oscillated slightly about its axis so as to eliminate any possible air bubbles in the solder and obtain as nearly as possible a perfect mechanical iit. Then the screw Il' is tightened and the parts are cooled slowly, so as to prevent the setting up of internal stresses.

It has been found by experience that the close ntting of the base of cone I 6 to the opposing surface of the head I I is an important factor. Compressional sound Waves striking against the head II are almost entirely reected from those parts of the head which are not solidly backed. The relatively massive cone I6, when connected to the head with a good t as described, affords a favorable acoustical impedance match, and the sound waves impinging upon the part of the head backed by the cone proceed in the direction of the axis of the cone and toward its apex or reduced end. The taper of the cone I6 apparently enhances the local intensity of the waves.

At its apex end, the cone is finished off with an external shoulder I8 against which one end of a nickel tube I9 is closely fitted, a reduced extension of the cone extending into and closely engaging the inner Wall of the tube. The tube I9 may be held in position on the cone by a ring of soft solder 2D around the junction.

Surrounding the cone I6 and spaced therefrom is a housing comprising a frustro-conical shield 22 surmounted by a cylindrical shield 23, the two shields being joined in any suitable manner, as by means of a ring of solder 24. At its base, the shield 22 is connected tothe inner face of the head II in concentric relation to cone I6, as by means of a Weld 22a. The inner end of the shiel 23 is closed by a cap 25 having a flange which ts closely around the shield. Near the juncture of the shield members 22 and 23 is an internal, shelflike, annular ring 26 which fits closely in the shield 23 and is staked thereto, as shown at 2l. A spool 28 made of insulating material is suppgrted on the shelf 26 and has a winding or coil 2 tube I9 and is held in position against the shelf 26 by a spacer 30 under the cap 25. Lead wires 3l from the coil 29 extend outwardly through a recess 32 in the spacer and through an aligned slot 33 in the shield 23.

Within the nickel tube I9 is a permanent bar magnet 35, which may be made of alnico or other suitable material, the magnet being loosely supported in any -convenient manner. As shown, one end of the magnet 35 is seated on the reduced end of cone I67 and the other end of the magnet terminates short of the outer end of tube I9. The field of the magnet 35 completes its circuit partly through the Walls of the nickel tube I9, and, therefore, the magnetic attraction causes the magnet to cling to the inner face of the tube. It will be apparent that there is no direct mechanical contact connection between the tube I9 and the shield 23, or only a loose contact connection, except that both are supported by the head I I.

The congressional Waves transmitted through the Water against the part of head II ladjacent cone I set up waves in the head, and these Waves enter the cone and proceed along its axis toward its apex end. The Waves continue into and along the nickel tube I9 and cause corresponding Vstresses of alternating compression and tension along the length of the tube. The high frequency of the Waves and the inertia of the tube I9 are The spool 28 fits loosely around the nickel such that a corresponding magnetostriction effect is produced in the tube. That is, the effect of these stresses is to generate a corresponding magnetic fleld in the tube I9, Which is superimposed upon the steady eld due to the magnet 35. To a great extent, the return path of the alternating flux is not through the magnet 35 but is through the air around coil 29. In other words, the alternating flux generated by the Waves of compression and tension in the nickel tube I9 links with the coil 29 and generates -a corresponding electromotive force therein. Thus, the energy of the Waves transmitted through the Water against the head I I is received by the microphone and converted into electromotive forces in the coil 29.

It will be apparent that the new magnetostrictive microphone may be readily assembled and is of rugged construction. The shield 22--23 not only serves to support the coil 29 independently of the nickel tubeI9 and the magnet 35, but also protects the cone I6 Iand the parts mounted thereon from the high explosive charge which is packed around the fuze I3 in the head.

We claim:

A directionally selective microphone for receiving compressional Waves through a metallic Wall, which comprises a generally conical member connected at its base to said Wall, a frustoconical shield secured at its base to said wall and surrounding said member, a magnetostriction tube connected to the reduced end portion of the conical member and disposed coaXially thereof, a cylindrical shield surmounting said frusto-conical shield and containing said tube, a, coil extending around the tube and supported by said cylindrical shield independently of the tube and the conical member, and a polarizing magnet within the tube.

CECIL K. STEDMAN. FREDERICK H. SMITH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,834,498 Parshall Dec. 1, .1931 1,882,401 Pierce Oct. ll, 1932 2,044,807 Noyes June 23, 1936 2,116,522 Kunze May 10, 1938 2,170,206 Mason Aug. 22, 1939 2,415,407 Benioff Feb. 11, 1947 FOREIGN PATENTS Number Country Date 405,613 Great Britain Jan. 26, 1934 

